standard.openDir
Displays a file dialog window to get a directory path on the local file system.
Syntax
ui.Interface.frontCall("standard", "openDir",
 [path,caption], [result]) 
- path - The default path of the directory like "/tmp".
 - caption - The caption to be displayed.
 - result - The name of the selected directory (or 
NULLif canceled). 
Usage
When invoking the "openDir" front call, the front-end displays the file dialog
window using the local file system, to let the end user enter a directory path.
The "openDir" front call is only supported with GDC front-end for desktop
applications. This front call is not supported on mobile or, for web applications with GAS.
The file dialog window rendering and features depend on the type of front end and the type of the front end platform (desktop OS, web browser).
If the user cancels the dialog, the front call returns NULL in the result
variable.
When specifying a file path, pay attention to platform specific rules regarding
directory separators and space characters in filenames. When the front-end executes on a recent Microsoft™ Windows™
system, you can use the / slash character as directory separator, like on Unix
systems. A directory or filename can contain spaces, and there is no need to surround the path with
double quotes in such case. When using backslash directory separators, make sure to escape backslash
characters in string literals with \\. 
Example
MAIN
    DEFINE rec RECORD
                path STRING,
                caption STRING
           END RECORD
    DEFINE result STRING
    LET rec.path = "/tmp"
    LET rec.caption = "Select directory"
    CALL ui.Interface.frontCall("standard","openDir",[rec.*],[result])
    IF result IS NULL THEN
       DISPLAY "No directory was selected."
    ELSE
       DISPLAY "Directory :", result
    END IF
END MAIN